This invention relates to friction supporting stays of the type which are used for supporting windows and sometimes doors, the stay being of the kind which comprises a track, a slider movable along the track, a strut pivotally connected to the track, a brace pivotally connected between the slider and the strut, a link pivotally connected to the slider and a bar pivotally connected to the link and the strut, the arrangement being such that as the slider moves along the track the bar can swing from a position overlying the track to a position where it is angled with respect to the track.
Control of the frictional restraint of the slider in known friction stays is achieved by use of a friction pad located between the slider and the track and a grub screw (i.e. in the nature of a set screw) threaded in the body of the slider and adapted to bear directly on the friction pad so that the frictional engagement between the slider and the track may be varied. The pad bears downwardly on the base of the track which is where the frictional engagement occurs.
An object of the present invention is to provide an improved form of slider which is cheaper to produce, can be made without any metal parts if desired, and is efficient in operation.
In accordance with the present invention, there is provided a slider for a track, said slider comprising a slider body adapted to be slidably received in the track, and said body including a recess having mounted therein a cam which is rotatable so as to bear against the sides of the recess, whereby to vary the frictional engagement of the slider with the track.
Also provided in accordance with the present invention is a friction stay comprising a track, a slider comprising a slider body movable along the track, a strut pivotally connected to the track, a brace pivotally connected between the slider and the strut, a link pivotally connected to the slider and a bar pivotally connected to the link and to the strut, the arrangement being such that as the slider moves along the track the bar can swing from a position overlying the track to a position where it is angled with respect to the track, characterized in that the slider body includes a recess having mounted therein a cam which is rotatable so as to bear against the sides of the recess, whereby to vary the frictional engagement of the slider with the track.
In one embodiment, the track is of channel section, and rotation of the cam to bear against the sides of the recess causes the longitudinal edges of the slider to bear against the walls of the channel. The walls of the channel may be flanged, and the longitudinal edges of the slider may be adapted to receive said flanges.
The slider body is preferably formed from a plastics material. Acetal homopolymers and copolymers are particularly preferred because of their low friction, low wear properties.
The cam may also be made from a plastics material such as an acetal homopolymer or copolymer. Alternatively, the cam may be made from a metal such as brass, steel or a zinc alloy of the kind sold under the trademark Mazak. If desired, the cam may be zinc plated to improve corrosion resistance.
The cam preferably forms a friction fit in the recess, so that it is rotatable against the friction between the two parts, but not freely rotatable. If necessary, friction between the cam and the slider body may be increased by knurling or otherwise roughening one or both of the cooperating surfaces. For example, if a metal cam is received in an acetal slider body, the cooperating surface of the cam may conveniently be provided with knurling in a saw-tooth pattern to a depth of 0.1 mm, with a pitch of 0.2 mm. If both the cam and the slider body are formed from an acetal resin, knurling is not generally necessary.
The cam may be arranged with a downwardly projecting boss on which there is a flange engageable in a corresponding hole in the lower part of the slider body so that the cam clicks (i.e. snappably fits) into and is held in place in the slider body.
Preferably there is a drive recess or slot in the cam to enable it to be rotated and thus to vary the pressure on the sides of the recess. The recess or slot may be e.g. a hexagonal or square recess or a screwdriver slot.
In one embodiment the slider body is scalloped at its outer edges adjacent the recess so that when the cam applies pressure to the internal walls of the recess the scalloped portions tend to be straightened thus bringing a straight portion of the slider body into contact with the adjacent walls of the track. Alternatively a straight sided slider may be used or slots may be formed in the ends of the walls to allow the outwardly facing portions of the walls to bow outwardly.
The cam may, for example, be symmetrical and have two parallel straight portions joined by French curves.